arXiv subjects

Irene Tamborra

Publications and source records attributed to Irene Tamborra.

At least 19 recordsLinked to original sources

arXiv2026

Flavor Conversion Enhances or Suppresses Supernova Explodability Independent of the Progenitor Mass

Flavor conversion can affect the neutrino-driven delayed explosion mechanism of collapsing massive stars, altering the efficiency of shock revival. We perform core-collapse supernova simulations in spherical symmetry for a set of progenitors with masses of $9.75\, M_\odot$, $11\, M_\odot$, $16.5\, M_\odot$, $28\, M_\odot$, $40\, M_\odot$, and $60\, M_\odot$, accounting for a mixing-length treatment for convection. Flavor conversion is modeled assuming instantaneous flavor equipartition below a critical baryon density, while conserving the lepton number. Regardless of the progenitor compactness, its mass, or the nuclear equation of state, we find that flavor conversion can increase heating (cooling) and enhance (hinder) the supernova explosion, if triggered near the gain (neutrino decoupling) region. Our findings suggest that the interplay among the region of the supernova core where flavor conversion occurs, the progenitor properties, and the nuclear equation of state is crucial in determining the fate of explosion and the properties of the compact remnant.

astro-ph.HE↗

arXiv2026

Neutrino Flavor Conversion Shapes the Rate of Failed Core-collapse Supernovae

The relative rate of neutron stars and black holes produced by the collapse of massive stars is highly uncertain. We simulate the stellar collapse of $195$ progenitors with masses between $9\, M_\odot$ and $120\, M_\odot$, incorporating a schematic treatment of neutrino flavor conversion. We find that flavor transformation reshapes the explodability of massive stars-especially in the $16$-$30\, M_\odot$ mass range-and modifies the compact remnant mass distribution. Our findings identify neutrino flavor conversion as a fundamental ingredient in predicting neutron star and black hole populations, while naturally easing the red-supergiant and the supernova-rate problems, as well as reconciling theoretical expectations with the low-mass tail of the observed neutron star mass distribution.

astro-ph.HE↗

arXiv2026

Unveiling Neutrino Nature with the Diffuse Supernova Background

The true nature of neutrinos--whether Dirac or Majorana--is a foundational, unresolved question. We demonstrate that the diffuse supernova neutrino background (DSNB) offers an untapped avenue to resolve this issue, provided neutrino magnetic moments are $\gtrsim 10^{-14}μ_B$. The intense magnetic fields characteristic of a subset of collapsing massive stars can trigger resonant chirality flips. This flavor conversion physics alters DSNB fluxes in measurable ways that depend on the neutrino nature. A $20$~yr combined exposure at Hyper-Kamiokande loaded with gadolinium and JUNO can unravel this signature at $90\%$ ($99\%$) confidence if the fraction of magnetorotational events exceeds $12\%$ ($20\%$) of cosmic core collapses. This result holds independent of the mass ordering and establishes the DSNB as a critical gateway to unveiling the true identity of the neutrino.

astro-ph.HE↗

arXiv2026

Interacting Supernovae: a Radio and X-ray Strategy to Constrain the Structure of the Circumstellar Medium

The interaction of supernova (SN) ejecta with the dense circumstellar medium (CSM) converts shock kinetic energy into radiation across multiple wavebands. We investigate the dependence of the X-ray and radio emission on the CSM geometry, considering spherical, hourglass, and disk shapes for the CSM. We find that the spectral and light-curve properties, both in X-ray and radio, significantly differ for spherical and non-spherical CSM structures. For a non-spherical CSM, the radio light curve flattens out near the peak frequency, due to efficient free-free absorption by the unshocked CSM. Moreover, the early rise of the radio light curve is shallower when the CSM density along the observer line of sight is larger than that in other directions. If the CSM density is lower along the observer line of sight, the radio light curve flattens near its peak, and the reverse-shock component is negligible in X-rays. Building on these features, we provide a method to constrain the CSM structure based on the rising part the radio light curve in the proximity of its peak; we show that the decay part of the radio light curve, after its peak, carries insight on whether the CSM density profile is wind-like or not. We further adopt the X-ray signal to corroborate the information extracted from radio. We test our strategy on SN 1993j and SN 2023ixf. For both SNe, we find that an asymmetric CSM is in excellent agreement with radio and X-ray observations and provides a viable alternative to non-wind scenarios suggested in the literature. Our findings highlight the crucial insight provided by radio and X-ray signals into the mass-loss history of the SN progenitor.

astro-ph.HE↗

arXiv2026

Quasi-steady flavor configuration of multi-energy neutrino ensembles

Neutrino flavor conversion profoundly impacts the explosion mechanism and multi-messenger emissions of core-collapse supernovae. Yet, state-of-the-art hydrodynamic simulations of neutrino-dense astrophysical environments cannot account for neutrino quantum kinetics, necessitating subgrid schemes to model the impact of neutrino self-interaction on the quasi-steady-state flavor configuration. We present semi-analytical approximations for the outcomes of both slow and fast flavor conversions in quasi-homogeneous systems with periodic boundary conditions. Independent of the mass ordering, our ansatz demonstrates excellent agreement with multi-angle and multi-energy solutions of the neutrino kinetic equations across a wide range of representative (anti)neutrino distributions.

astro-ph.HE↗

arXiv2026

Diffuse Neutrino Background from Magnetorotational Stellar Core Collapses

A statistically significant detection of the diffuse supernova neutrino background (DSNB) is around the corner. To this purpose, we assess the contribution to the DSNB of magnetorotational collapses of massive stars, relying on a suite of state-of-the-art three-dimensional neutrino-magnetohydrodynamic simulations. We find that neutrinos from magnetorotational core collapses boost the high-energy tail of the DSNB spectrum, similar to what is expected from neutrino-driven black hole-forming collapses. The latest data from the Super-Kamiokande Collaboration can already exclude that more than $9\%$ of all collapsing massive stars undergo magnetorotational collapses under optimistic assumptions. A DSNB detection at $3 σ$ could take place up to $4$ yr earlier at Super-Kamiokande-Gadolinium or JUNO if the fraction of magnetorotational collapses should be larger than $10\%$. Fascinatingly, if the fraction of magnetorotational stellar collapses should be larger than $19\%$ ($13\%$), Hyper-Kamiokande could measure such a fraction at $3σ$ after ($10$ yr) $20$ yr of DSNB data taking. The combination of DSNB and electromagnetic data has the potential to resolve the degenerate contributions from magnetorotational and neutrino-driven black hole-forming collapses, providing crucial insight on the properties of the population of collapsing massive stars.

astro-ph.HE↗

arXiv2026

Detection horizon for the neutrino burst from the stellar helium flash

Low-mass stars ($M\lesssim 2\,M_\odot$) ignite helium under degenerate conditions, eventually causing a nuclear run-away -- the helium flash. The alpha-capture process on $^{14}$N produces a large amount of $^{18}$F, whose subsequent decay spawns an intense $ν_e$ burst (with average energy of $0.38$ MeV) lasting about a day. We show that, in addition, a strong $1.7$ MeV neutrino line is generated by electron capture on $^{18}$F. Detection is hindered by large backgrounds in state-of-the-art neutrino observatories, such as JUNO. In next-generation facilities, such as the Jinping neutrino experiment, the horizon for a detection with a local significance of $3 σ$ would be extended to almost $3$ pc. Although helium flashes occur a few times per year in our Galaxy, there are no stellar candidates approaching the tip of the red giant branch within $10$ pc. Hence, to date, asteroseismology remains the most promising tool for probing the most energetic thermonuclear event in the life of a low-mass star.

astro-ph.SR↗

arXiv2026

Matter- and magnetically-driven flavor conversion of neutrinos in magnetorotational collapses

The magnetorotational collapse of massive stars copiously emits neutrinos of all flavors, with a prominent hierarchy between the non-electron and electron flavor average energies. Relying on a three-dimensional neutrino-magnetohydrodynamic simulation of a $13 M_\odot$ progenitor, we investigate flavor conversion in matter. We find that, in addition to resonant flavor conversion of neutrinos and antineutrinos in matter, (anti)neutrinos experience chirality-flipping interactions due to their non-zero magnetic moment ($μ\lesssim 10^{-12} μ_B$) and large magnetic field in the source ($B \simeq 10^{15}$ G). For Majorana neutrinos, this leads to resonant flavor-changing neutrino-antineutrino mixing. The event rate expected from a Galactic collapse at current and next-generation neutrino telescopes, such as IceCube and Hyper-Kamiokande, strongly depends on the orientation of the magnetorotational collapse with respect to the observer direction and flavor conversion scenario. The event rate is expected to be larger for an observer facing head on the jet launched during the stellar collapse and peaks around $400$-$600$ ms after bounce. Our work highlights that understanding the rich phenomenology of flavor conversion in magnetorotational collapses is essential to take full advantage of the joint detection of neutrinos and gravitational waves from these sources.

astro-ph.HE↗

arXiv2026

Magnetized Shocks Mediated by Radiation from Leptonic and Hadronic Processes

Shocks in astrophysical transients are key sites of particle acceleration. If the shock upstream is optically thick, radiation smoothens the velocity discontinuity at the shock (radiation-mediated shocks). However, in mildly magnetized outflows, a collisionless subshock can form, enhancing the efficiency of particle acceleration. We solve the hydrodynamic equations of a steady-state, radiation-mediated shock together with the radiative transfer equations accounting for electron and proton acceleration. Our goal is to explore the impact of the magnetic field and non-thermal radiation on the shock structure and the resulting spectral distribution of photons. To this purpose, we assume a relativistic upstream fluid velocity ($Γ_u = 10$) and investigate shock configurations with variable upstream magnetization ($σ_u = 0$, $10^{-8}$, $10^{-4}$, $0.1$, and $0.3$). We find that synchrotron self-absorption alters the shock profile for $σ_u \gtrsim 10^{-8}$, with resulting changes up to $100\%$ in the bulk Lorentz factor at the shock; for $σ_u \gtrsim 0.1$, a prominent subshock forms. The spectral energy distributions of upstream- and downstream-going photons are also altered. Radiative processes linked to accelerated protons are responsible for a high-energy ($\gtrsim 10$ GeV) tail in the photon spectrum; however, the radiation flux and pressure are negligibly affected with consequent minor impact on the shock structure. Our work highlights the importance of coupling the shock hydrodynamics to the transport of photons, electrons, protons, and intermediate particles to forecast the multi-messenger emission from astrophysical transients.

astro-ph.HE↗

arXiv2025

Neutrino quantum kinetics in three flavors

The impact of neutrino flavor conversion on the supernova mechanism is yet to be fully understood. We present multi-energy and multi-angle solutions of the neutrino quantum kinetic equations in three flavors, without employing any attenuation term for the neutrino self-interaction strength and taking into account neutrino advection and non-forward collisions with the background medium. Flavor evolution is explored within a spherically symmetric shell surrounding the region of neutrino decoupling in the interior of a core-collapse supernova, relying on the output of a spherically symmetric core-collapse supernova model with a progenitor mass of $18.6 M_\odot$. We select two representative post-bounce times: $t_{\rm pb} = 0.25$ s (no angular crossings are present and flavor conversion is triggered by slow collective effects) and $t_{\rm pb} = 1$ s (angular crossings trigger fast flavor instabilities). We find that flavor equipartition is achieved for the late post-bounce time ($t_{\rm pb} = 1$ s), where the (anti)neutrino emission properties among different flavors tend to approach each other. In this case, $\barν_e$ tends to $\barν_x = (\barν_μ+ \barν_τ)/2$ and a similar trend holds for neutrinos. However, flavor equipartition does not occur for our early post-bounce time ($t_{\rm pb} = 0.25$ s). Accounting for weak-magnetism corrections, crossings in the $μ$ and $τ$ lepton number angular distributions arise; however, such crossings have a magnitude smaller than the one occurring in the electron sector and negligibly affect flavor evolution. Because of flavor conversion, the neutrino heating rate increases up to $30\%$ with respect to the case where flavor conversion is neglected.

astro-ph.HE↗

arXiv2025

Collapsar Disk Outflows III: Detectable Neutrino and Gravitational Wave Signatures

We investigate the neutrino and gravitational wave (GW) signals from accretion disks formed during the failed collapse of a rotating massive star (a collapsar). Following black hole formation, a neutrino-cooled, shocked accretion disk forms, which displays non-spherical oscillations for a period of seconds before becoming advective and exploding the star. We compute the neutrino and GW signals (matter quadrupole, frequencies $\lesssim 100$ Hz) from collapsar disks using global axisymmetric, viscous hydrodynamic simulations. The neutrino signal with typical energies of O$(10)$ MeV is maximal during the neutrino-cooled (NDAF) phase that follows shock formation. This phase lasts for a few seconds and is easily detectable within O$(10-100)$ kpc by the IceCube Neutrino Telescope. Additional neutrino signatures from a precursor equatorial shock and by stochastic accretion plumes during the advective phase are detectable within the galaxy. The GW signal during the NDAF phase is detectable in the galaxy by current and next-generation ground-based observatories. The explosion (memory) GW signal is similar to that of standard core-collapse supernovae and can be probed with a deci-Hertz space-based detector. Shock oscillations during the NDAF phase impart time variations with frequency O$(10-100)$ Hz to the neutrino and GW signals, encoding information about the shock dynamics and inner disk. These time variations can be detectable in neutrinos by IceCube within O$(1-10)$ kpc depending on progenitor model, flavor transformation scenario, and detailed properties of the angular momentum transport mechanism.

astro-ph.HE↗

arXiv2025

Neutrinos from stars in the Milky Way

Neutrinos are produced during stellar evolution by means of thermal and thermonuclear processes. We model the cumulative neutrino flux expected at Earth from all stars in the Milky Way: the Galactic stellar neutrino flux (GS$ν$F). We account for the star formation history of our Galaxy and reconstruct the spatial distribution of Galactic stars by means of a random sampling procedure based on Gaia Data Release 2. We use the stellar evolution code $\texttt{MESA}$ to compute the neutrino emission for a suite of stellar models with solar metallicity and zero-age-main-sequence mass between $0.08M_\odot$ and $100\ M_\odot$, from their pre-main sequence phase to their final fates. We then reconstruct the evolution of the neutrino spectral energy distribution for each stellar model in our suite. The GS$ν$F lies between $\mathcal{O}(1)$ keV and $\mathcal{O}(10)$ MeV, with thermal (thermonuclear) processes responsible for shaping neutrino emission at energies smaller (larger) than $0.1$ MeV. Stars with mass larger than $\mathcal{O}(1\ M_\odot)$, located in the thin disk of the Galaxy, provide the largest contribution to the GS$ν$F. Moreover, most of the GS$ν$F originates from stars distant from Earth about $5-10$ kpc, implying that a large fraction of stellar neutrinos can reach us from the Galactic Center. Solar neutrinos and the diffuse supernova neutrino background have energies comparable to those of the GS$ν$F, challenging the detection of the latter. However, directional information of solar neutrino and GS$ν$F events, together with the annual modulation of the solar neutrino flux, could facilitate the GS$ν$F detection; this will kick off a new era for low-energy neutrino astronomy, also providing a novel probe to discover New Physics.

astro-ph.SR↗

arXiv2025

Steady state of fast-oscillating neutrinos in an inhomogeneous medium

The streaming of neutrinos in an inhomogeneous medium is known to affect the physics of flavor conversion. We employ an ensemble of single-crossed angular distributions and explore the physics of flavor conversion, while neutrinos propagate across a one-dimensional inhomogeneous medium. The advective term in the neutrino equations of motion is responsible for the cascade of flavor waves towards ever smaller spatial and angular scales. However, as the system evolves, perturbations with large wavenumbers are damped, with a resulting smearing of the flavor configuration. We provide a simple recipe that allows to forecast the steady-state flavor configuration achieved by neutrinos without solving their kinetic equations. In particular, we find that flavor equipartition on one side of the angular spectrum and the cancellation of the spectral crossing in the lepton number distributions, proposed in the literature as generic flavor outcome, is a special solution depending on the degree of neutrino-antineutrino asymmetry. This work constitutes a step forward towards the development of semi-analytic schemes to account for flavor conversion physics in hydrodynamic simulations of core-collapse supernovae and neutron-star merger remnants.

astro-ph.HE↗

arXiv2025

Diagnosing electron-neutrino lepton number crossings in core-collapse supernovae: A comparison of methods

Fast neutrino flavor conversion may impact the explosion mechanism and nucleosynthesis in core-collapse supernovae. A necessary condition for fast flavor conversion is the presence of crossings in the angular distribution of the electron-neutrino lepton number (ELN) crossing. Because of the computational costs, flavor-dependent angular distributions are not computed by the vast majority of state-of-the-art hydrodynamical simulations; instead, angular distributions are reconstructed employing approximate methods in post-processing. In this work, we evaluate the performance of four methods adopted to diagnose the existence of ELN crossings. For selected post-bounce times, we extract the fluid and thermodynamic properties from spherically symmetric supernova simulations for an $18.6 M_\odot$ progenitor, testing cases with and without muons as well as with and without mixing-length treatment of proto-neutron star convection. We compare the occurrence of crossings in the angular distributions obtained by solving the Boltzmann equations with those in distributions reconstructed from angular moments of our Boltzmann solutions by using the maximum entropy and Minerbo schemes, and also with crossings identified via a polynomial weighting function applied to the angular moments. Our results show that the polynomial method and the Minerbo closure scheme have severe limitations. The maximum entropy approach captures most of the forward crossings, although it fails to reproduce or misidentifies crossings in a subset of our models. These findings highlight the need for robust modeling of the neutrino angular properties in order to assess the impact of flavor conversion on the supernova mechanism.

astro-ph.HE↗

arXiv2025

Electron-neutrino lepton number crossings: Variations with the supernova core physics

A crucial ingredient affecting fast neutrino flavor conversion in core-collapse supernovae (SNe) is the shape of the angular distribution of the electron-neutrino lepton number (ELN). The presence of an ELN crossing signals favorable conditions for flavor conversion. However, the dependence of ELN crossings on the SN properties is only partially understood. We investigate a suite of 12 spherically symmetric neutrino-hydrodynamics simulations of the core collapse of a SN with a mass of $18.6 M_\odot$; each model employs different microphysics (i.e., three different nuclear equations of state, with and without muon creation) and includes or not a mixing-length treatment for proto-neutron star convection. We solve the Boltzmann equations to compute the neutrino angular distributions relying on static fluid properties extracted from each of the SN simulations in our suite for six selected post-bounce times. We explore the dependence of the ELN distributions on the SN microphysics and proto-neutron star convection. We find that the latter shifts the proto-neutron star radius outwards, favoring the appearance of ELN crossings at larger radii. On the other hand, muon creation causes proto-neutron star contraction, facilitating the occurrence of ELN crossings at smaller radii. These effects mildly depend on the nuclear equation of state. Our findings highlight the subtle impact of the SN microphysics, proto-neutron star convection, and neutrino transport on the ELN angular distributions.

astro-ph.HE↗

arXiv2025

Neutrinos from explosive transients at the dawn of multi-messenger astronomy

With the advent of time-domain astronomy and the game-changing next generation of telescopes, we have unprecedented opportunities to explore the most energetic events in our Universe through electromagnetic radiation, gravitational waves, and neutrinos. These are elementary particles, which exist in three different flavors and change the latter as they propagate in the dense core of astrophysical sources as well as en route to Earth. To capitalize on existing and upcoming multi-messenger opportunities, it is crucial to understand: 1. the role of neutrinos in explosive transient sources as well as in the synthesis of the elements heavier than iron; 2. the impact of neutrino physics on the multi-messenger observables; 3. the information on the source physics carried by the detectable neutrino signal. In this review, the status of this exciting and fast-moving field is outlined, focusing on astrophysical sources linked to collapsing massive stars and neutron-star mergers. In light of the upcoming plethora of multi-messenger data, outstanding open issues concerning the optimization of multi-messenger detection strategies are discussed.

astro-ph.HE↗

arXiv2025

Pauli blocking: probing beyond-mean-field effects in neutrino flavor evolution

Neutrino quantum kinetics in dense astrophysical environments is investigated relying on the mean-field approximation. In this paper, we heuristically explore whether beyond-mean-field effects due to neutrino degeneracy could hinder flavor instabilities that are otherwise foreseen. Our results show that these corrections shift the stability regions for a suite of (anti)neutrino ensembles: the flavor conversion of previously unstable distributions can be damped, but angular distributions that are stable in the mean-field case can also become unstable. Our work should serve as a motivation to further investigate the limitations of the mean-field treatment.

astro-ph.HE↗

arXiv2025

Identifying Thorne-Żytkow Objects through Neutrinos

Thorne-Żytkow Objects (TŻOs) have been predicted to form when a neutron star is engulfed by a diffuse, convective giant envelope. Accretion onto a neutron star at a rate that is larger than $10^{-4}\, M_\odot$ yr$^{-1}$ is expected to lead to significant emission of neutrinos of all flavors with energy of $1$-$100$ MeV. Since the neutrino signal is expected to largely vary in time (from milliseconds to thousands of years), we outline detection strategies tailored to the signal duration. We find that neutrino detection from TŻOs up to the Small Magellanic Cloud is within the reach of current- and next-generation neutrino observatories, such as Super- and Hyper-Kamiokande, the IceCube Neutrino Observatory, and JUNO. Interestingly, if targeted searches for neutrinos from TŻO candidates (e.g.VX Sgr in our Galaxy as well as HV 2112 and HV 11417 in the Small Magellanic Cloud) should lead to positive results, neutrinos could positively identify the nature of such sources and their accretion rate. Furthermore, the diffuse supernova neutrino background may be able to rule out extreme scenarios for the formation and accretion rates of TŻOs. Our findings should serve as motivation for establishing dedicated searches for neutrino emission from TŻOs. This is especially timely since it is challenging to detect TŻOs via electromagnetic radiation unambiguously, and the TŻO gravitational wave signal could be probed with next-generation detectors for sources within our Galaxy only.

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